Abstract: A system for directly driving light emitting diodes (LEDs). A string of LEDs is coupled across an input voltage and includes a plurality of separate groups of LEDs. Each of a plurality of switches is coupled in parallel with an associated one of the groups of LEDs for controlling current flow through the associated group of LEDs in response to a control signal from a controller circuit. A switch protection circuit is associated with at least one of the switches. The switch protection circuit is configured to place the switch into a conducting state in the event of failure of an LED in the associated group of LEDs.

Abstract: A system for directly driving light emitting diodes (LEDs). A string of LEDs is coupled across an input voltage and includes a plurality of separate groups of LEDs. Each of a plurality of switches is coupled in parallel with an associated one of the groups of LEDs for controlling current flow through the associated group of LEDs in response to a control signal from a controller circuit. A switch protection circuit is associated with at least one of the switches. The switch protection circuit is configured to place the switch into a conducting state in the event of failure of an LED in the associated group of LEDs.

Abstract: A method of making a mercury-free fluorescent lamp in which a layer of phosphor particles are applied to an exterior surface of the lamp envelope, includes preparing a sol-gel precursor solution that, when dried, leaves a sol-gel residue material, such as thin film SiO2, that coats the phosphor particles and resists removal of the phosphor particles from the exterior surface, dipping the envelope into the sol-gel precursor solution, and, after removing the envelope from the solution, drying the sol-gel precursor solution to form a network of the sol-gel residue material on the exterior surface that meshes with the layer of phosphor particles. The sol-gel residue material attaches the phosphor particles to the exterior surface with sufficient strength so that the lamp can be handled as if the layer of phosphor particles were on the interior of the envelope.

Abstract: By controlling the temperature of a glass reservoir tube attached to a closed vapor cell, the vapor pressure inside the cell can be accurately controlled. The apparatus for controlling the reservoir temperature includes an electric heater, a temperature sensor, heat straps to distribute and remove heat from the reservoir, and a clamp to hold the apparatus in close thermal contact with the exterior of the reservoir. An external control circuit energizes the reservoir heater as required. In the preferred embodiment the vapor cell functions as an optical filter when filled with a heated metallic vapor such as cesium. The reservoir tube functions as the cold spot of the cell and contains a small pool of the metal in liquid form.This invention was made with Government support under N66001-86-R-0050 awarded by the Department of the Navy. The Government has certain rights in this invention.